[aws|beanstalk] Added #load_balancer method.

Added a convenience method to get the load balancer model associated
with the beanstalk environment.

lib/fog/aws/models/beanstalk/environment.rb

@@ -45,6 +45,12 @@ module Fog
           data
         end
 
+        # Returns the load balancer object associated with the environment.
+        def load_balancer(elb_connection = Fog::AWS[:elb])
+          requires :resources
+          elb_connection.load_balancers.get(resources['LoadBalancer']['LoadBalancerName'])
+        end
+
         # Return events related to this version
         def events
           requires :id